Corona discharge device

ABSTRACT

In a corona discharge device wherein corona discharge is established between a fine corona discharge electrode and a counter electrode, a vibration suppression member is positioned between the corona discharge electrode and the counter electrode for preventing transverse vibration of the corona discharge electrode by electrostatic force.

United States Patent Fnruichi et al. [451 Apr. 11, 1972 [54] CORONA DISCHARGE DEVICE [72] Inventors: Mssayoshi Furuichi, Tokyo; Seiichi [56] References Cited Miyakawa, Chiba; Nobuchika Masuda, UNITED STATES PATENTS Tokyo, all of Japan 3,470,417 9/1969 G1bbons ..3l7/4 Asslgnw Katsuragawa Denki Kabushiki Kaisha, 3,581,149 5/1971 Tanaka et a1. ..317/4 Ota-ku, Tokyo-to, Japan Primary Examiner-L. T. Hix [22] Flled' 1971 Attorney-Bosworth, Sessions, Herrstrom & Cain [21] App]. No.: 110,697

. [57] ABSTRACT [30] Foreign Application Priority Data In a corona discharge device wherein corona discharge is established between a fine corona discharge electrode and a Jan. 29, 1970 Japan ..45/7856 counter l t d a vibration suppression member 15 p081- tioned between the corona discharge electrode and the [52] "317/4, 317/262 250/495 ZC counter electrode for preventing transverse vibration of the [51] Int. Cl ..G03g 15/02, l-lOlt 19/00 corona discharge electrode by electrostatic force [58] Field of Search ..3l7/2 F, 4, 262 A;

250/495 GC, 49.5 ZC, 49.5 TC 7 Claims, 8 Drawing Figures CORONA DISCGE DEVICE BACKGROUND OF THE INVENTION This invention relates to a corona discharge device.

Corona discharge devices are widely used in various industrial fields such as electrophotographic machines, printing machines, paper manufacturing machines or the like for depositing or neutralizing electrostatic charges. The corona discharge device utilized for these purposes generally comprises a corona discharge electrode in the form of fine metal wires or rods and a counter electrode confronting the corona discharge electrode with an air gap. The width of the air gap is made generally small, a few millimeters, for the purpose of efficiently depositing the charge with relatively low voltage so that if the length of discharge electrode is long, say about one meter, the electrode tends to vibrate due to electrostatic attraction or mechanical vibration thus resulting in spark discharge or short circuiting between the corona discharge electrode and the counter electrode. Such spark discharge or short circuiting causes breakage of the corona discharge electrode. For this reason it is necessary to provide some means for preventing such vibration of the corona discharge electrode.

SUMMARY OF THE INVENTION It is therefore an object of this invention to provide means intermediate the corona discharge electrode and the counter electrode for preventing vibration of the corona discharge electrode by electrostatic force. Another object of this invention is to provide an improved corona discharge device wherein corona discharge is established uniformly along the length of the corona discharge electrode.

According to this invention, there is provided a fine corona discharge electrode and a counter electrode for establishing corona discharge between said corona discharge electrode and said counter electrode characterized in that a vibration suppression member is positioned between said corona discharge electrode and said counter electrode and substantially parallel thereto for preventing transverse vibration of said corona discharge electrode by electrostatic force.

BRIEF DESCRIPTION OF THE DRAWING In the accompanying drawing:

FIG. 1 shows a side view of one embodiment of this invention;

FIG. 2 shows a cross-sectional view of the corona discharge device shown in FIG. 1; and

FIG. 3 to FIG. 8 diagrammatically show modified embodiments of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiment of this invention shown in FIGS. 1 and 2 relates to a corona discharge device adapted to deposit a charge on the surface of a photosensitive element 10 for use in electrophotography and to project a light image upon the element through the corona discharge device. As shown, a plu rality of spaced apart parallel vertical counter electrodes 2 are secured at their opposite ends to two insulative side frames 1, and corona discharge electrodes 3 in the form of fine metal wires are provided between counter electrodes 2 and parallel thereto. If desired, a control grid 4 may be provided between the counter electrodes and the photosensitive element 10. In operation, as shown in FIG. 2, the counter electrodes 2 are grounded and a high DC voltage of suitable polarity or an AC voltage is impressed upon the corona discharge electrodes 3 to create corona discharges between respective corona discharge electrodes and counter electrodes whereby to deposit a charge on the surface of photosensitive element 10. The quantity of the charge deposited can be controlled by control grid 4 energized by a suitable source of potential 6.

The corona discharge device thus far described is of the conventional type. According to this invention, vibration suppressing members 7 made of insulating material or metal wires coated with electric insulative material are disposed between corona discharge electrodes 3 and corresponding counter electrodes 2 in parallel therewith, with the opposite ends of the suppressing members mechanically secured to side frames 1. This arrangement of the suppressing members effectively limits transverse vibration of the corona discharge electrodes 3 thus preventing spark discharge or short circuiting mentioned above between the corona discharge electrodes and the counter electrode.

Although the precise theory of operation of the vibration suppressing members 7 for electrically preventing the spark discharge is not clear we present the following explanation. The potential gradients near the corona discharge electrodes are substantially identical whether the vibration suppression members 7 are used or not provided that the corona discharge electrodes are held stationary. In the absence of the vibration suppressing members, however, when the corona discharge electrode are moved transversely, the potential gradients near the corona discharge electrodes increase on one side on which the distance between the corona discharge electrodes and the counter electrodes has decreased whereas the potential gradients decrease on the opposite side on which the distance between these electrodes has increased, thus attracting the corona discharge electrodes towards the counter electrodes on said first mentioned side. This will cause spark discharge or short circuiting between the corona discharge electrodes and the counter electrodes. However, in the presence of the vibration suppressing members, upon transverse movement of the corona discharge electrodes, as the corona discharge electrodes approach the vibration suppression members on said first mentioned side, the potential gradient near the corona discharge electrodes decreases due to the action of electrostatic charging. The electrostatic charge on the vibration suppressing members, having the same polarity as that of the potential of the corona discharge electrodes, applies a repulsive force upon the corona discharge electrodes thus suppressing their transverse vibration. Thus it will be clear that the suppressing members of this invention suppress the vibration of the corona discharge electrodes by electrostatic force and not by mechanical damping action. For this reason, it is not necessary to precisely align the corona discharge electrodes and the vibration suppressing members. When the vibration suppression members are not made of an electric insulator having sufficiently high mechanical strength such as nylon, for example, it is necessary to use reinforcing metal cores.

A corona discharge unit was actually manufactured utilizing corona discharge electrodes each having a length of one meter and a diameter of 0.06 mm and wherein the spacings between each corona discharge electrode and the counter electrodes on both sides thereof were 7.5 mm and a vibration suppressing member of nylon of a diameter of 0.3 mm was interposed at substantially the mid point between each corona discharge electrode and counter electrode. It was found that due to the presence of the vibration suppressing members although it was necessary to slightly increase by a (few percent) the potential impressed upon the corona discharge electrodes for depositing the same quantity of charge as in the case not utilizing the vibration suppressing members, there was no noticeable vibration of the corona discharge electrodes. Moreover, in the prior art corona discharge device there is a tendency of concentrating the corona discharge on dirt deposited on the corona discharge electrodes or on surface irregularities thereof, thus causing irregular discharge along the length of the electrodes. However, the presence of the vibration suppression members greatly decreases such tendency probably due to the electrostatic shielding effect thereof.

It should be understood that the number and position of the vibration suppressing members are not limited to those illustrated hereinabove. Thus for example, the relative arrangements of the corona discharge electrode 3 and vibration suppression members 7 shown in FIGS. 3, 4 and 5 are effective to prevent vibrations of the corona discharge electrode in both vertical and horizontal directions. When there are a plurality of corona discharge electrodes 3 between adjacent counter electrodes, as shown in FIG. 6, vibration suppressing members 7 are provided between each corona discharge electrode and a counter electrode cooperating therewith. Where a transparent conductive glass plate 11 such as Nesa glass is used as the counter electrode as shown in FIG. 7, corona discharge electrodes 3 and vibration suppressing members 7 may be arranged in two staggered parallel rows. Further, where it is not necessary to project a light image through the corona discharge device, the counter electrode 2 may take the form of an inverted cup shape as shown in FIG. 8 in which vibration suppressing members 7 are disposed between one corona discharge electrode 3 and three sides of the counter electrode. It will be clear that in this invention it is not always necessary to dispose the corona discharge electrode at the geometrical center of the vibration suppressing members as shown in FIGS. 3 and 4 but may be displaced slightly therefrom.

Thus, it will be clear that this invention provides an improved corona discharge device capable of efficiently preventing the vibration of the corona discharge electrode by simple means. Although the invention has been shown and described in terms of corona discharge devices for use in electrophotography, it is evident that the novel corona discharge device can also be used in many other fields where it is necessary to deposit or neutralize electrostatic charges.

We claim:

1. In a corona discharge device of the class comprising a fine corona discharge electrode and a counter electrode for establishing corona discharge between said corona discharge electrode and said counter electrode, the improvement which comprises a vibration suppression member positioned between said corona discharge electrode and said counter electrode and substantially parallel thereto for preventing transverse vibration of said corona discharge electrode by electrostatic force.

2. The corona discharge device according to claim 1 wherein said vibration suppression members are made of electric insulating material.

3. The corona discharge device according to claim 1 wherein said vibration suppressing members comprise metal wires coated with insulating films.

4. The corona discharge device according to claim 1 which is constructed to transmit light therethrough.

5. The corona discharge device according to claim 1 wherein said counter electrode comprises a plurality of spaced apart vertical metal electrodes, said corona discharge electrode is positioned intermediate each pair of adjacent metal electrodes and said suppressing members are disposed between said corona discharge electrode and said pair of metal electrodes.

6. The corona discharge device according to claim 1 wherein said counter electrode comprises a flat sheet of conductive glass and said vibration suppressing members and a plurality of corona discharge electrodes are disposed in two parallel rows on one side of said conductive glass, said vibration suppressing members and said corona discharge electrodes being staggered with respect to each other.

7. The corona discharge device according to claim 1 wherein said counter electrode takes the form of an inverted cup and said corona discharge electrode and said vibration suppressing members are disposed in said inverted cup. 

1. In a corona discharge device of the class comprising a fine corona discharge electrode and a counter electrode for establishing corona discharge between said corona discharge electrode and said counter electrode, the improvement which comprises a vibration suppression member positioned between said corona discharge electrode and said counter electrode and substantially parallel thereto for preventing transverse vibration of said corona discharge electrode by electrostatic force.
 2. The corona discharge device according to claim 1 wherein said vibration suppression members are made of electric insulating material.
 3. The corona discharge device according to claim 1 wherein said vibration suppressing members comprise metal wires coated with insulating films.
 4. The corona discharge device according to claim 1 which is constructed to transmit light therethrough.
 5. The corona discharge device according to claim 1 wherein said counter electrode comprises a plurality of spaced apart vertical metal electrodes, said corona discharge electrode is positioned intermediate each pair of adjacent metal electrodes and said suppressing members are disposed between said corona discharge electrode and said pair of metal electrodes.
 6. The corona discharge device according to claim 1 wherein said counter electrode comprises a flat sheet of conductive glass and said vibration suppressing members and a plurality of corona discharge electroDes are disposed in two parallel rows on one side of said conductive glass, said vibration suppressing members and said corona discharge electrodes being staggered with respect to each other.
 7. The corona discharge device according to claim 1 wherein said counter electrode takes the form of an inverted cup and said corona discharge electrode and said vibration suppressing members are disposed in said inverted cup. 